The following patents and/or commonly assigned patent applications are hereby incorporated herein by reference:
This invention relates to the field of display systems, more particularly to display systems using sequential color techniques such as color wheels.
Modern display systems typically create full-color projected images by projecting three single-color images. The eye of the viewer integrates these single-color images to give the perception of a single, full-color image. Three separate modulators or controllable light sources are often used simultaneously to generate the primary-color images. For example, three liquid crystal display (LCD) panels or digital micromirror device (DMD) arrays and appropriate dichroic filters create three primary-color images using a single light source, or three cathode ray tubes perform both the modulator and light source functions to create three primary-color images.
Alternatively, a single modulator is used with a sequential color light source to sequentially create three primary-color images. If the light source sequences through the primary colors fast enough, the viewer will not see the sequential single-color images but instead will see a single full-color image. A sequential color light source is formed by combining a white-light source with a filtering means such as a color wheel.
A color wheel typically is a disk-shaped assembly of dichroic filters. Other shapes of xe2x80x9ccolor wheelsxe2x80x9d are possible, such as rotating drums or polygons. The white-light beam is focused on the color wheel and the dichroic filters, which are either transmissive or reflective, filter the white light to form a primary-color light beam. The color wheel includes at least one filter for each of the primary colors.
Spinning the color wheel so that each filter passes through the point at which the white light beam strikes the color wheel generates a sequential primary color light beam. The color wheel typically is spun fast enough to create at least one primary color period for each primary during each frame of a video image. Spinning the wheel faster, or using multiple filter segments for one or more of the primary colors can reduce color separation artifacts that allow the viewer to detect the sequential color nature of the display system.
While a sequential color display system typically costs less to produce than a simultaneous color display system, images created by a sequential filtered color display system are not as bright as images created by simultaneous color display systems using the same light source. This is because at any given time only a portion of the light generated by the light source is being used to form the image. For example, when using a three-color equal-segment filter wheel, each primary color is produced only ⅓ of the time. Additionally, when a sequential filter such as a color wheel is used, the light during the filter transitions, typically called spoke times, will be a varying mixture of the two filters being changed in and out. This mixed-color light cannot be modulated using red, green, and blue primary color data without adversely affecting the color purity of the created image.
High image brightness is one of the major desires of customers in the projection display market. In addition to a bright image, consumers desire saturated colorsxe2x80x94specially when displaying computer generated graphics. Because of the limited dwell time of each color, bright saturated images are difficult to produce using sequential color systems. Additionally, insertion of a white or clear segment makes colors dimmer, less bright, relative to the white areas of the displayed image. Therefore, a method and system for increasing the brightness of the secondary color components (yellow, cyan, and magenta) in a projected image is needed.
Objects and advantages will be obvious, and will in part appear hereinafter and will be accomplished by the present invention which provides a method and system for using spoke light, that is light generated during color filter transitions, to increase the brightness of the secondary colors. Some embodiments include additional filter segments that can increase the saturation of the secondary colors produced by the display. One embodiment of the claimed invention provides a method of producing secondary colors in a primary color display system. The method comprises: receiving a color data word for an image pixel; determining a secondary color value of said color data word; and enabling a spatial light modulator during a transition period for a period dependent on said secondary color value. According to one embodiment, at least one primary color value is reduced to offset partially the increased intensity of the secondary color value. Various embodiments utilize more than one transition period is optionally used to increase the secondary intensity and limit the application of the secondary color boost to pixels with low white content.
According to yet another embodiment of the disclosed invention, a display system is provided. The display system comprising a modulated sequential color light source and a controller. The controller receives a color data word corresponding to each pixel in a desired image, determines a secondary color value of the color data word, and enables the modulated sequential color light source during a transition period for a period dependent on the secondary color value. The modulated sequential color light source typically is comprised of a sequential color light source and a spatial light modulator. The spatial light modulator to receives a sequential color light beam from the sequential color light source and modulates the light beam based on image data received from the controller. The sequential color light source typically is comprised of a white light source for generating a beam of white light and a sequential color filter for temporally filtering the white light beam to create a sequential color light beam. The sequential color filter typically is a set of filters forming a rotating color wheel.